Pyrolysis or so-called carbonization of coal is widely known. As disclosed in U.S. Pat. No. 4,104,129 which issued to Fields et al on Aug. 1, 1978, coal may be heated at elevated temperatures of 500.degree. C.-1500.degree. C. to thereby convert it to solid carbonaceous residue known as char, gaseous products containing significant amount of hydrogen and liquid containing large proportions of aromatics and heterocyclics. The process is generally known as coal carbonization or pyrolysis. The Field et al patent describes a coal carbonization-desulfurization process for reducing the sulfur content of the coal to produce a low sulfur coal which is more acceptable commercially and less objectionable environmentally.
The hydrocarbons produced from coal pyrolysis are usually of low economic value due to their high carbon-to- hydrogen ratio and their tendency to self-polymerize because of presence of olefinic and acetylenic hydrocarbons. U.S. Pat. No. 4,162,959 which issued to Kandaswamy Duraiswamy on July 31, 1979 describes a method whereby the low value hydrocarbon products of coal pyrolysis may be upgraded, thereby improving the economy of coal pyrolysis. The process described in this patent initially involves oxidation of a carbonaceous material in an oxidation zone to produce hot particulate char. This hot char is then reacted with steam in a conversion zone to produce hydrogen. The hot char and hydrogen so produced are then combined with carbonaceous material and the carbonaceous material is pyrolyzed with steam, in the presence of hydrogen, in a pyrolysis zone. The steam is injected into the pyrolysis zone to produce more hydrogen for use in hydrogenating the volatilized hydrocarbons.
Other patents of interest include U.S. Pat. Nos. 3,481,834; 3,960,700; 3,997,423; 4,012,311; 4,013,543; 4,189,374; 4,206,033; 4,213,826 and 4,218,303. These patents and the patents referred to therein are by no means exhaustive but are representative of the numerous patents and publications which relate, in one way or another, to coal carbonization, pyrolysis or liquefaction. In general, in order to obtain more valuable liquid hydrocarbons from coal carbonization, the prior art methods either resort to catalytic processes, hydropyrolysis (i.e., pyrolysis in the presence of hydrogen) or combination of these methods. It can be appreciated, therefore, that any such process which does not require a catalyst and whereby increased yields of liquid hydrocarbons (synthetic liquid fuels) can be obtained without a hydrogen feed gas, offers a more attractive alternative from practical and commercial standpoints.
Accordingly, it is an object of this invention to provide a method for liquefaction of coal to obtain liquid hydrocarbons having substantial fuel value, e.g., synthetic liquid fuels, or more simply "synfuels".
It is a further object of this invention to provide a method involving pyrolysis of coal whereby large yields of liquid hydrocarbons are obtained without the use of a catalyst.
It is still another object of this invention to provide an improved coal pyrolysis process whereby large yields of synfuels are obtained without resorting to an external source of hydrogen gas.
The foregoing and other objects, features and advantages of this invention will be more fully appreciated from the following detailed description of the invention and the accompanying drawings.